Pyrrolo[3,2-d]pyrimidine derivatives as inducers of human interferon

ABSTRACT

Compounds of formula (I) and salts thereof: 
     
       
         
         
             
             
         
       
     
     wherein R 1  is hydrogen, methyl or —(CH 2 ) 2 OR 3 , R 2  is methyl or —(CH 2 ) 2 OR 4 , or R 1  and R 2 , together with the nitrogen atom to which they are attached, are linked to form a 5- or 6-membered heterocyclyl wherein the 6-membered heterocyclyl is optionally substituted by two hydroxy substituents; R 3  and R 4  are each independently hydrogen or methyl; and n is an integer having a value of 5 or 6, are inducers of human interferon. Compounds which induce human interferon may be useful in the treatment or prevention of various disorders, for example the treatment or prevention of allergic diseases and other inflammatory conditions, for example allergic rhinitis and asthma, infectious diseases and cancer, and may also be useful as vaccine adjuvants.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to compounds, processes for their preparation, compositions containing them, to their use in the treatment or prevention of various disorders in particular allergic diseases and other inflammatory conditions for example allergic rhinitis and asthma, infectious diseases, and cancer, and as vaccine adjuvants.

BACKGROUND OF THE INVENTION

Vertebrates are constantly threatened by the invasion of microorganisms and have evolved mechanisms of immune defence to eliminate infective pathogens. In mammals, this immune system comprises two branches; innate immunity and acquired immunity. The first line of host defence is the innate immune system, which is mediated by macrophages and dendritic cells. Acquired immunity involves the elimination of pathogens at the late stages of infection and also enables the generation of immunological memory. Acquired immunity is highly specific, due to the vast repertoire of lymphocytes with antigen-specific receptors that have undergone gene rearrangement.

Central to the generation of an effective innate immune response in mammals are mechanisms which bring about the induction of interferons and other cytokines which act upon cells to induce a number of effects. In man, the type I interferons are a family of related proteins encoded by genes on chromosome 9 and encoding at least 13 isoforms of interferon alpha (IFNα) and one isoform of interferon beta (IFNβ). Interferon was first described as a substance which could protect cells from viral infection (Isaacs & Lindemann, J. Virus Interference. Proc. R. Soc. Lon. Ser. B. Biol. Sci. 1957: 147, 258-267). Recombinant IFNα was the first approved biological therapeutic and has become an important therapy in viral infections and in cancer. As well as direct antiviral activity on cells, interferons are known to be potent modulators of the immune response, acting on cells of the immune system (Gonzalez-Navajas J. M. et al Nature Reviews Immunology, 2012; 2, 125-35).

Toll-like receptors (TLRs) are a family of ten Pattern Recognition Receptors described in man (Gay, N. J. et al, Annu. Rev. Biochem., 2007: 46, 141-165). TLRs are expressed predominantly by innate immune cells where their role is to monitor the environment for signs of infection and, on activation, mobilise defence mechanisms aimed at the elimination of invading pathogens. The early innate immune-responses triggered by TLRs limit the spread of infection, while the pro-inflammatory cytokines and chemokines that they induce lead to recruitment and activation of antigen presenting cells, B cells, and T cells. The TLRs can modulate the nature of the adaptive immune-responses to give appropriate protection via dendritic cell-activation and cytokine release (Akira S. et al, Nat. Immunol., 2001: 2, 675-680). The profile of the response seen from different TLR agonists depends on the cell type activated.

TLR7 is a member of the subgroup of TLRs (TLRs 3, 7, 8, and 9), localised in the endosomal compartment of cells which have become specialised to detect non-self nucleic acids. TLR7 plays a key role in anti-viral defence via the recognition of ssRNA (Diebold S. S. et al, Science, 2004: 303, 1529-1531; and Lund J. M. et al, PNAS, 2004: 101, 5598-5603). TLR7 has a restricted expression-profile in man and is expressed predominantly by B cells and plasmacytoid dendritic cells (pDC), and to a lesser extent by monocytes. Plasmacytoid DCs are a unique population of lymphoid-derived dendritic cells (0.2-0.8% of Peripheral Blood Mononuclear Cells (PBMCs)) which are the primary type I interferon-producing cells secreting high levels of interferon-alpha (IFNα) and interferon-beta (IFNβ) in response to viral infections (Liu Y-J, Annu. Rev. Immunol., 2005: 23, 275-306).

Administration of a small molecule compound which could stimulate the innate immune response, including the activation of type I interferons and other cytokines via Toll-like receptors, could become an important strategy for the treatment or prevention of human diseases. Small molecule agonists of TLR7 have been described which can induce interferon alpha in animals and in man (Takeda K. et al, Annu. Rev. Immunol., 2003: 21, 335-76). TLR7 agonists include imidazoquinoline compounds such as imiquimod and resiquimod, oxoadenine analogues and also nucleoside analogues such as loxoribine and 7-thia-8-oxoguanosine which have long been known to induce interferon alpha (Czarniecki. M., J. Med, Chem., 2008: 51, 6621-6626; Hedayat M. et al, Medicinal Research Reviews, 2012: 32, 294-325). This type of immunomodulatory strategy has the potential to identify compounds which may be useful in the treatment of allergic diseases (Moisan J. et al, Am. J. Physiol. Lung Cell Mol. Physiol., 2006: 290, L987-995), viral infections (Horcroft N. J. et al, J. Antimicrob. Chemther, 2012: 67, 789-801), cancer (Krieg A., Curr. Oncol. Rep., 2004: 6(2), 88-95), other inflammatory conditions such as irritable bowel disease (Rakoff-Nahoum S., Cell., 2004, 23, 118(2): 229-41), and as vaccine adjuvants (Persing et al. Trends Microbiol. 2002: 10(10 Suppl), S32-7). More specifically, allergic diseases are associated with a Th2-biased immune-response to allergens. Th2 responses are associated with raised levels of IgE, which, via its effects on mast cells, promotes a hypersensitivity to allergens, resulting in the symptoms seen, for example, in asthma and allergic rhinitis. In healthy individuals the immune-response to allergens is more balanced with a mixed Th2/Th1 and regulatory T cell response. TLR7 ligands have been shown to reduce Th2 cytokine and enhance Th1 cytokine release in vitro and to ameliorate Th2-type inflammatory responses in allergic lung models in vivo (Duechs M. J., Pulmonary Pharmacology & Therapeutics, 2011: 24, 203-214; Fili L. et al, J. All. Clin. Immunol., 2006: 118, 511-517; Tao et al, Chin. Med. J., 2006: 119, 640-648; Van L. P. Eur. J. Immunol., 2011: 41, 1992-1999). Thus TLR7 ligands have the potential to rebalance the immune-response seen in allergic individuals and lead to disease modification. Recent clinical studies with the TLR7 agonist have shown repeated intranasal stimulation of TLR7 to produce a sustained reduction in the responsiveness to allergen in patients with both allergic rhinitis and allergic asthma (Greiff L. Respiratory Research, 2012: 13, 53; Leaker B. R. et al, Am. J. Respir. Crit. Care Med., 2012: 185, A4184).

In the search for novel small molecule inducers of human interferon IFNα an assay strategy has been developed to characterise small molecule (regardless of mechanism) which is based on stimulation of primary human donor cells or whole blood with compounds, and is disclosed herein.

SUMMARY OF THE INVENTION

In a first aspect, the present invention is directed to compounds of formula (I) and salts thereof:

Certain compounds of the invention have been shown to be inducers of human interferon and may possess a desirable developability profile compared to known inducers of human interferon. In one embodiment, certain compounds of the invention may show selectivity for IFNα with respect to TNFα. In a further embodiment, certain compounds of the invention may be desirable for development because they may be less potent than other inducers of human interferon.

Compounds which induce human interferon may be useful in the treatment or prevention of various disorders, for example the treatment or prevention of allergic diseases and other inflammatory conditions, for example allergic rhinitis and asthma, the treatment or prevention of infectious diseases and cancer. Accordingly, the invention is further directed to pharmaceutical compositions comprising a compound of formula (I), or a pharmaceutically acceptable salt thereof. The present invention is further directed to methods of treatment or prevention of disorders associated therewith using a compound of formula (I) or a pharmaceutically acceptable salt thereof, or a pharmaceutical composition comprising a compound of formula (I) or a pharmaceutically acceptable salt thereof.

The compounds of the invention may also have use as vaccine adjuvants. Consequently, the present invention is further directed to a vaccine composition comprising a compound of formula (I), or a pharmaceutically acceptable salt thereof, and an antigen or antigen composition.

Certain compounds of the invention may be potent immunomodulators and accordingly, care should be exercised in their handling.

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect, the present invention is directed to compounds of formula (I) and salts thereof:

wherein:

-   -   R¹ is hydrogen, methyl or —(CH₂)₂OR³,     -   R² is methyl or —(CH₂)₂OR⁴, or     -   R¹ and R², together with the nitrogen atom to which they are         attached, are linked to form a 5- or 6-membered heterocyclyl         wherein the 6-membered heterocyclyl is optionally substituted by         two hydroxy substituents;     -   R³ and R⁴ are each independently hydrogen or methyl; and     -   n is an integer having a value of 5 or 6.

In one embodiment, R¹ is hydrogen, methyl or —(CH₂)₂OR³, and R² is methyl or —(CH₂)₂OR⁴. In another embodiment, R¹ is hydrogen and R² is —(CH₂)₂OR⁴, for example —(CH₂)₂OH. In another embodiment, R¹ and R² are both methyl. In a further embodiment, R¹ is —(CH₂)₂OR³ and R² is —(CH₂)₂OR⁴.

In one embodiment, R¹ and R², together with the nitrogen atom to which they are attached, are linked to form a 5- or 6-membered heterocyclyl wherein the 6-membered heterocyclyl is optionally substituted by two hydroxy substituents. In another embodiment, R¹ and R², together with the nitrogen atom to which they are attached, are linked to form pyrrolidine. In another embodiment, R¹ and R², together with the nitrogen atom to which they are attached, are linked to form piperidine optionally substituted by two hydroxy substituents. In a further embodiment, R¹ and R², together with the nitrogen atom to which they are attached, are linked to form piperidine-3,5-diol.

In one embodiment, when R¹ is —(CH₂)₂OR³ and R² is —(CH₂)₂OR⁴, R³ and R⁴ are both hydrogen. In another embodiment, when R¹ is —(CH₂)₂OR³ and R² is —(CH₂)₂OR⁴, R³ is hydrogen and R⁴ is methyl. In a further embodiment, when R¹ is —(CH₂)₂OR³ and R² is —(CH₂)₂OR⁴, R³ and R⁴ are both methyl.

In one embodiment, n is 5. In a further embodiment, n is 6.

Examples of compounds of formula (I) are provided in the following list, and form a further aspect of the invention:

-   2,6-dimethyl-7-(6-(piperidin-1-yl)hexyl)-5H-pyrrolo[3,2-d]pyrimidin-4-amine; -   2,6-dimethyl-7-(5-(pyrrolidin-1-yl)pentyl)-5H-pyrrolo[3,2-d]pyrimidin-4-amine; -   2,2′-((5-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)pentyl)azanediyl)diethanol; -   2,2′-((6-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)azanediyl)diethanol; -   2-((6-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)(2-methoxyethyl)amino)ethanol; -   7-(6-(bis(2-methoxyethyl)amino)hexyl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine; -   2-((6-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)amino)ethanol; -   (3R,5S)-1-(6-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)piperidine-3,5-diol; -   (3R,5R)-1-(6-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)piperidine-3,5-diol;     and -   7-(6-(dimethylamino)hexyl)-2,6-dimethyl-5H-pyrrolo[3,2-]pyrimidin-4-amine; -   and salts thereof.

As used herein, the term “heterocyclyl” refers to a monocyclic saturated heterocyclic ring containing the specified number of carbon atoms and one heteroatom, which heteroatom is nitrogen. Such heterocyclic rings are pyrrolidine or piperidine.

It is to be understood that references herein to compounds of the invention mean a compound of formula (I) as the free base, or as a salt, for example a pharmaceutically acceptable salt.

In one aspect of the invention, a compound of formula (I) is in the form of a free base. In a further aspect of the invention, a compound of formula (I) is in the form of a pharmaceutically acceptable salt.

Salts of the compounds of formula (I) include pharmaceutically acceptable salts and salts which may not be pharmaceutically acceptable but may be useful in the preparation of compounds of formula (I) and pharmaceutically acceptable salts thereof. In one aspect of the invention, a compound of formula (I) is in the form of a pharmaceutically acceptable salt. Salts may be derived from certain inorganic or organic acids.

Examples of salts are pharmaceutically acceptable salts. Pharmaceutically acceptable salts include acid addition salts. For a review on suitable salts see Berge et al., J. Pharm. Sci., 66:1-19 (1977).

Examples of pharmaceutically acceptable acid addition salts of a compound of formula (I) include inorganic acids such as, for example, hydrochloric acid, hydrobromic acid, orthophosphoric acid, nitric acid, phosphoric acid, or sulphuric acid, or with organic acids such as, for example, methanesulphonic acid, ethanesulphonic acid, p-toluenesulphonic acid, acetic acid, propionic acid, lactic acid, citric acid, fumaric acid, malic acid, succinic acid, salicylic acid, maleic acid, glycerophosphoric acid, tartaric, benzoic, glutamic, aspartic, benzenesulphonic, naphthalenesulphonic such as 2-naphthalenesuphonic, hexanoic acid or acetylsalicylic acid.

The invention includes within its scope all possible stoichiometric and non-stoichiometric forms of the salts of the compounds of formula (I).

Salts may be formed using techniques well-known in the art, for example by precipitation from solution followed by filtration, or by evaporation of the solvent.

Typically, a pharmaceutically acceptable acid addition salt can be formed by reaction of a compound of formula (I) with a suitable acid (such as hydrobromic, hydrochloric, sulphuric, maleic, p-toluenesulphonic, methanesulphonic, naphthalenesulphonic or succinic acids), optionally in a suitable solvent such as an organic solvent, to give the salt which is usually isolated for example by crystallisation and filtration.

It will be appreciated that many organic compounds can form complexes with solvents in which they are reacted or from which they are precipitated or crystallised. These complexes are known as “solvates”. For example, a complex with water is known as a “hydrate”. Solvents with high boiling points and/or solvents with a high propensity to form hydrogen bonds such as water, ethanol, iso-propyl alcohol, and N-methyl pyrrolidinone may be used to form solvates. Methods for the identification of solvated include, but are not limited to, NMR and microanalysis. Solvates of the compounds of formula (I) are within the scope of the invention. As used herein, the term solvate encompasses solvates of both a free base compound as well as any salt thereof.

Certain of the compounds of the invention may contain chiral atoms and hence may exist in one or more stereoisomeric forms. The present invention encompasses all of the stereoisomers of the compounds of the invention, including optical isomers, whether as individual stereoisomers or as mixtures thereof including racemic modifications. Any stereoisomer may contain less than 10% by weight, for example less than 5% by weight, or less than 0.5% by weight, of any other stereoisomer. For example, any optical isomer may contain less than 10% by weight, for example less than 5% by weight, or less than 0.5% by weight, of its antipode.

Certain of the compounds of the invention may exist in tautomeric forms. It will be understood that the present invention encompasses all of the tautomers of the compounds of the invention whether as individual tautomers or as mixtures thereof.

The compounds of the invention may be in crystalline or amorphous form. Furthermore, some of the crystalline forms of the compounds of the invention may exist as polymorphs, all of which are included within the scope of the present invention. The most thermodynamically stable polymorphic form or forms of the compounds of the invention are of particular interest.

Polymorphic forms of compounds of the invention may be characterised and differentiated using a number of conventional analytical techniques, including, but not limited to, X-ray powder diffraction (XRPD), infrared spectroscopy (IR), Raman spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and solid-state nuclear magnetic resonance (ssNMR).

The present invention also includes all suitable isotopic variations of a compound of formula (I) or a pharmaceutically acceptable salt thereof. An isotopic variation of a compound of formula (I), or a pharmaceutically acceptable salt thereof, is defined as one in which at least one atom is replaced by an atom having the same atomic number but an atomic mass different from the atomic mass usually found in nature. Examples of isotopes that can be incorporated into compounds of the invention include isotopes of hydrogen, carbon, nitrogen, oxygen, fluorine and chlorine such as ²H, ³H, ¹³C, ¹⁴C, ¹⁵N, ¹⁷O, ¹⁸O, ¹⁸F and ³⁶Cl, respectively. Certain isotopic variations of a compound of formula (I) or a salt or solvate thereof, for example, those in which a radioactive isotope such as ³H or ¹⁴C is incorporated, are useful in drug and/or substrate tissue distribution studies. Tritiated, i.e., ³H, and carbon-14, i.e., ¹⁴C, isotopes are particularly preferred for their ease of preparation and detectability. Further, substitution with isotopes such as deuterium, i.e., ²H, may afford certain therapeutic advantages resulting from greater metabolic stability, for example, increased in vivo half-life or reduced dosage requirements and hence may be preferred in some circumstances. Isotopic variations of a compound of formula (I), or a pharmaceutically salt thereof, can generally be prepared by conventional procedures such as by the illustrative methods or by the preparations described in the Examples hereafter using appropriate isotopic variations of suitable reagents.

It will be appreciated from the foregoing that included within the scope of the invention are solvates, hydrates, isomers and polymorphic forms of the compounds of formula (I) and salts and solvates thereof.

Compound Preparation

The compounds of formula (I) and salts thereof may be prepared by the methodology described hereinafter, constituting further aspects of this invention.

Accordingly, there is provided a process for the preparation of a compound of formula (I), or a salt thereof:

wherein R¹, R² and n are as defined hereinbefore, which process comprises the deprotection of a compound of formula (II):

wherein R¹, R² and n are as defined hereinbefore for a compound of formula (I) and PG is a protecting group, such as benzyloxymethyl (BOM) or p-toluenesufonyl, and thereafter, if required, preparing a salt of the compound of formula (I).

For example, a compound of formula (II) wherein PG is equivalent to BOM is dissolved in a suitable solvent, for example methanol or ethanol, and passed over a suitable catalyst, for example 10% palladium on carbon in the presence of hydrogen, at a suitable temperature, for example 20-60° C. in a suitable flow hydrogenation apparatus such as the Thales H-cube™. The product (I) is isolated by removal of the solvent and purification if required.

A compound of formula (II) may be prepared by reaction of a compound of formula (III):

wherein R¹, R² and n are as hereinbefore defined for a compound of formula (II) and PG is a protecting group with hydrogen in the presence of a catalyst.

For example a compound of formula (III) is dissolved in a suitable solvent for example methyl alcohol or ethyl alcohol, and passed over a suitable catalyst, for example 10% palladium on carbon, in the presence of hydrogen at a suitable temperature, for example 20-60° C., in a suitable flow hydrogenation apparatus such as the Thales H-Cube™. The product (II) is isolated by removal of the solvent and purification, if required.

When the protecting group is the benzyloxymethyl (BOM) group the reaction to reduction the alkyne can result in the simultaneous removal of the protecting group to afford compounds of formula (I) directly.

A compound of formula (III) may be prepared by reaction of a compound of formula (IV):

wherein Y is a leaving group for example a halogen such as iodine or bromine or an alkyl sulfonate such as a trifluoromethane sulfonate and PG is a protecting group with a compound of formula (V):

wherein R¹, R² and n are defined for a compound of formula (I).

For example a compound of formula (IV) and a compound of formula (V) are dissolved in a suitable solvent, for example N,N-dimethylformamide, in the presence of copper(I) iodide, a suitable catalyst, for example bis(triphenylphosphine)palladium(II) dichloride and a suitable base, for example triethylamine, and heated at a suitable temperature, for example 20-55° C. for a suitable period of time, for example 0.5-17 hours. The product (III) is isolated after an aqueous work-up and purification.

A compound of formula (V) may be prepared by reaction of a compound of formula (VI):

wherein n is defined for a compound of formula (I) and X is a leaving group such as a halogen, for example chlorine, bromine or iodine, or an alkyl sulfonate, for example p-toluenesulfonate, with a compound of formula (VII):

wherein R¹ and R² are as defined for a compound of formula (I).

For example a compound of formula (VI) and a compound of formula (VII) and a suitable base, for example sodium hydrogen carbonate, are dissolved in a suitable solvent, for example N,N-dimethylformamide, and heated at a suitable temperature, for example 80-100° C. for a suitable period of time, for example 16-18 hours. The product (V) is isolated after aqueous work-up and purification, for example by isolation of a suitable crystalline salt, for example the oxalate salt.

Compounds of formula (VI) and formula (VII) are either commercially available or may be prepared by methods described in the literature.

Alternatively a compound of formula (III) may be prepared by reaction of a compound of formula (VIII):

wherein n is hereinbefore defined for a compound of formula (I), X is a leaving group as defined for compounds of formula (VI) and PG is a protecting group with a compound of formula (VII).

For example a compound of formula (VIII), a compound of formula (VII) and a suitable base, for example triethylamine, are dissolved in a suitable solvent, for example acetontrile and heated at a suitable temperature, for example 60-80° C. for a suitable period of time, for example 16-26 hours. The product (III) is isolated after an aqueous work-up and purification.

Compounds of formula (VIII) can be prepared by reaction of compounds of formula (IV) with compounds of formula (VI). For example a compound of formula (IV) and a compound of formula (VI) are dissolved in a suitable solvent, for example N,N-dimethylformamide, in the presence of copper(I) iodide, a suitable catalyst, for example bis(triphenylphosphine)palladium(II) dichloride and a suitable base, for example triethylamine, and heated at a suitable temperature, for example 65° C. for a suitable period of time, for example 18-20 hours. The product (VIII) is isolated after an aqueous work-up and purification.

Compounds of formula (IV) may be prepared by reaction of compounds of formula (IX):

wherein Y is defined for a compound of formula (IV) and PG is a protecting group with a solution of ammonia.

For example a solution of aqueous ammonia (0.88) is added to a solution of a compound of formula (IX) in a suitable solvent, for example iso-propyl alcohol. The resultant mixture is then heated in a microwave heater at a suitable temperature, for example 120-150° C. for a suitable period of time, for example 1-2 hours. The product (IV) is isolated after an aqueous work-up and purification.

Compounds of formula (IX) may be prepared by reaction of compounds of formula (X):

wherein Y is defined for a compound of formula (IV) with a compound of formula (XI):

wherein compound of formula (XI) is a suitable precursor to the protecting group PG, for example benzyl chloromethyl ether.

For example, a compound of formula (X) in a suitable solvent, for example N,N-dimethylformamide or tetrahydrofuran, is treated with a suitable base, for example a suspension of sodium hydride in oil. A compound of formula (XI), for example benzyl chloromethyl ether is added and the reaction mixture is stirred at a suitable temperature, for example 20° C. for a suitable period of time, for example 1-4 hours. The product (IX) is isolated after an aqueous work-up and purification.

Compounds of formula (X) may be prepared by reaction of compounds of formula (XII):

with a halogenating reagent, for example N-iodosuccinimide.

For example a compound of formula (XII) is dissolved in a suitable solvent, for example tetrahydrofuran, is reacted with N-iodosuccinimide at suitable temperature, for example 20° C. for a suitable period of time, for example 1-2 hours. The product (X) is isolated after an aqueous work-up and purification.

Compounds of formula (XII) may be prepared by reaction of compounds of formula (XIII):

with a chlorinating reagent, for example phosphorus oxychloride.

For example a compound of formula (XIII) is suspended in phosphorus oxychloride and heated at a suitable temperature, for example 90-120° C. for a suitable period of time, for example 3-30 hours. Excess phosphorus oxychloride may be removed in vacuo then the residue is poured onto ice and the pH of the mixture adjusted to 7-9. The product is then extracted into a suitable organic solvent, for example ethyl acetate. The product (XIII) is isolated by removal of the solvent and purification if required.

Compounds of formula (XIII) may be prepared by reaction of compounds of formula (XIV):

with a suitable base, for example sodium hydroxide.

For example a solution of compounds of formula (XIV) in a suitable solvent, for example ethyl alcohol, is treated with an aqueous solution of sodium hydroxide and the reaction mixture stirred at a suitable temperature, for example 80-100° C. for a suitable period of time, for example 2-18 hours. The product (XIII) is isolated after an aqueous work-up and purification.

Compounds of formula (XIV) can be prepared by reaction of compounds of formula (XV):

with acetonitrile.

For example, a suspension of a compound of formula (XV) in a acetontrile is treated with a solution of hydrogen chloride in a suitable solvent, for example a solution of hydrogen chloride in 1,4-dioxane and is heated at a suitable temperature, 50-70° C. for a suitable period of time, for example 16-96 hours. The product (XIV) is isolated after filtration.

Compounds of formulae (VI), (VII), (XI) and (XV) are either known in the literature or are commercially available, for example from Sigma-Aldrich, UK, or may be prepared by analogy with known procedures, for example those disclosed in standard reference texts of synthetic methodology such as J. March, Advanced Organic Chemistry, 6th Edition (2007), WileyBlackwell, or Comprehensive Organic Synthesis (Trost B. M. and Fleming I., (Eds.), Pergamon Press, 1991), each incorporated herein by reference as it relates to such procedures.

Examples of other protecting groups that may be employed in the synthetic routes described herein and the means for their removal can be found in T. W. Greene ‘Protective Groups in Organic Synthesis’, 4th Edition, J. Wiley and Sons, 2006, incorporated herein by reference as it relates to such procedures.

For any of the hereinbefore described reactions or processes, conventional methods of heating and cooling may be employed, for example temperature-regulated oil-baths or temperature-regulated hot-blocks, and ice/salt baths or dry ice/acetone baths respectively. Conventional methods of isolation, for example extraction from or into aqueous or non-aqueous solvents may be used. Conventional methods of drying organic solvents, solutions, or extracts, such as shaking with anhydrous magnesium sulphate, or anhydrous sodium sulphate, or passing through a hydrophobic frit, may be employed. Conventional methods of purification, for example crystallisation and chromatography, for example silica chromatography or reverse-phase chromatography, may be used as required. Crystallisation may be performed using conventional solvents such as ethyl acetate, methanol, ethanol, or butanol, or aqueous mixtures thereof. It will be appreciated that specific reaction times temperatures may typically be determined by reaction-monitoring techniques, for example thin-layer chromatography and LC-MS.

Where appropriate individual isomeric forms of the compounds of the invention may be prepared as individual isomers using conventional procedures such as the fractional crystallisation of diastereoisomeric derivatives or chiral high performance liquid chromatography (chiral HPLC).

The absolute stereochemistry of compounds may be determined using conventional methods, such as X-ray crystallography.

Methods of Use

Examples of disease states in which the compounds of formula (I) and pharmaceutically acceptable salts thereof have potentially beneficial effects include allergic diseases and other inflammatory conditions for example allergic rhinitis and asthma, infectious diseases, and cancer. The compounds of formula (I) and pharmaceutically acceptable salts thereof are also of potential use as vaccine adjuvants.

As modulators of the immune response the compounds of formula (I) and pharmaceutically acceptable salts thereof may also be useful in the treatment and/or prevention of immune-mediated disorders, including but not limited to inflammatory or allergic diseases such as asthma, allergic rhinitis and rhinoconjuctivitis, food allergy, hypersensitivity lung diseases, eosinophilic pneumonitis, delayed-type hypersensitivity disorders, atherosclerosis, pancreatitis, gastritis, colitis, osteoarthritis, psoriasis, sarcoidosis, pulmonary fibrosis, respiratory distress syndrome, bronchiolitis, chronic obstructive pulmonary disease, sinusitis, cystic fibrosis, actinic keratosis, skin dysplasia, chronic urticaria, eczema and all types of dermatitis.

The compounds of formula (I) and pharmaceutically acceptable salts thereof may also be useful in the treatment and/or prevention of reactions against respiratory infections, including but not limited to airways viral exacerbations and tonsillitis. The compounds may also be useful in the treatment and/or prevention of autoimmune diseases including but not limited to rheumatoid arthritis, psoriatic arthritis, systemic lupus erythematosus, Sjöegrens disease, ankylosing spondylitis, scleroderma, dermatomyositis, diabetes, graft rejection, including graft-versus-host disease, inflammatory bowel diseases including, but not limited to, Crohn's disease and ulcerative colitis.

The compounds of formula (I) and pharmaceutically acceptable salts thereof may also be useful in the treatment or prevention of infectious diseases including, but not limited to, those caused by hepatitis viruses (e.g. hepatitis B virus, hepatitis C virus), human immunodeficiency virus, papillomaviruses, herpesviruses, respiratory viruses (e.g. influenza viruses, respiratory syncytial virus, rhinovirus, metapneumovirus, parainfluenzavirus, SARS), and West Nile virus. The compounds of formula (I) and pharmaceutically acceptable salts thereof may also be useful in the treatment or prevention of microbial infections caused by, for example, bacteria, fungi, or protozoa. These include, but are not limited to, tuberculosis, bacterial pneumonia, aspergillosis, histoplasmosis, candidosis, pneumocystosis, leprosy, chlamydia, cryptococcal disease, cryptosporidosis, toxoplasmosis, leishmania, malaria, and trypanosomiasis.

The compounds of formula (I) and pharmaceutically acceptable salts thereof may also be useful in the treatment or prevention of various cancers, in particular the treatment or prevention of cancers that are known to be responsive to immunotherapy and including, but not limited to, renal cell carcinoma, lung cancer, breast cancer, colorectal cancer, bladder cancer, melanoma, leukaemia, lymphomas and ovarian cancer.

It will be appreciated by those skilled in the art that references herein to treatment refer to the treatment of established conditions. However, the compounds of formula (I) and pharmaceutically acceptable salts thereof may, depending on the condition, also be useful in the prevention of certain diseases. Thus, in one embodiment, there is provided the treatment or prevention of a disease. In another embodiment, there is provided the treatment of a disease. In a further embodiment, there is provided the prevention of a disease.

There is thus provided as a further aspect of the invention a compound of formula (I), or a pharmaceutically acceptable salt thereof, for use in therapy.

It will be appreciated that, when a compound of formula (I) or a pharmaceutically acceptable salt thereof is used in therapy, it is used as an active therapeutic agent.

There is also therefore provided a compound of formula (I), or a pharmaceutically acceptable salt thereof, for use in the treatment or prevention of allergic diseases and other inflammatory conditions, infectious diseases, and cancer.

There is also therefore provided a compound of formula (I), or a pharmaceutically acceptable salt thereof, for use in the treatment or prevention of allergic rhinitis.

There is also therefore provided a compound of formula (I), or a pharmaceutically acceptable salt thereof, for use in the treatment or prevention of asthma.

There is further provided the use of a compound of formula (I), or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for the treatment or prevention of allergic diseases and other inflammatory conditions, infectious diseases, and cancer.

There is further provided the use of a compound of formula (I), or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for the treatment or prevention of allergic rhinitis.

There is further provided the use of a compound of formula (I), or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for the treatment or prevention of asthma.

There is further provided a method of treatment or prevention of allergic diseases and other inflammatory conditions, infectious diseases, and cancer, which method comprises administering to a human subject in need thereof, a therapeutically effective amount of a compound of formula (I), or a pharmaceutically acceptable salt thereof.

There is further provided a method of treatment or prevention of allergic rhinitis, which method comprises administering to a human subject in need thereof, a therapeutically effective amount of a compound of formula (I), or a pharmaceutically acceptable salt thereof.

There is further provided a method of treatment or prevention of asthma, which method comprises administering to a human subject in need thereof, a therapeutically effective amount of a compound of formula (I), or a pharmaceutically acceptable salt thereof.

The compounds of formula (I) and pharmaceutically acceptable salts thereof are also of potential use as vaccine adjuvants.

There is thus provided as a further aspect of the invention a vaccine composition comprising a compound of formula (I), or a pharmaceutically acceptable salt thereof, and an antigen or antigen composition for use in therapy.

There is thus provided as a further aspect of the invention the use of a compound of formula (I), or a pharmaceutically acceptable salt thereof, and an antigen or antigen composition in the manufacture of a medicament for use in therapy.

There is further provided a method of treating or preventing disease comprising the administration to a human subject suffering from or susceptible to disease, a vaccine composition comprising a compound of formula (I), or a pharmaceutically acceptable salt thereof, and an antigen or antigen composition.

Compositions

The compounds of formula (I) and pharmaceutically acceptable salts thereof will normally, but not necessarily, be formulated into pharmaceutical compositions prior to administration to a patient. Accordingly, in another aspect of the invention there is provided a pharmaceutical composition comprising a compound of formula (I), or a pharmaceutically acceptable salt thereof, and one or more pharmaceutically acceptable excipients.

The compounds of formula (I) and pharmaceutically acceptable salts thereof may be formulated for administration in any convenient way. The compounds of formula (I) and pharmaceutically acceptable salts thereof may, for example, be formulated for oral, topical, inhaled, intranasal, buccal, parenteral (for example intravenous, subcutaneous, intradermal, or intramuscular) or rectal administration. In one aspect, the compounds of formula (I) and pharmaceutically acceptable salts thereof are formulated for oral administration. In a further aspect, the compounds of formula (I) and pharmaceutically acceptable salts thereof are formulated for topical administration, for example intranasal or inhaled administration.

Tablets and capsules for oral administration may contain conventional excipients such as binding agents, for example syrup, acacia, gelatin, sorbitol, tragacanth, mucilage of starch, cellulose or polyvinyl pyrrolidone; fillers, for example, lactose, microcrystalline cellulose, sugar, maize starch, calcium phosphate or sorbitol; lubricants, for example, magnesium stearate, stearic acid, talc, polyethylene glycol or silica; disintegrants, for example, potato starch, croscarmellose sodium or sodium starch glycollate; or wetting agents such as sodium lauryl sulphate. The tablets may be coated according to methods well known in the art.

Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for constitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, for example, sorbitol syrup, methyl cellulose, glucose/sugar syrup, gelatin, hydroxymethyl cellulose, carboxymethyl cellulose, aluminium stearate gel or hydrogenated edible fats; emulsifying agents, for example, lecithin, sorbitan mono-oleate or acacia; non-aqueous vehicles (which may include edible oils), for example almond oil, fractionated coconut oil, oily esters, propylene glycol or ethyl alcohol; or preservatives, for example, methyl or propyl p-hydroxybenzoates or sorbic acid. The preparations may also contain buffer salts, flavouring, colouring and/or sweetening agents (e.g. mannitol) as appropriate.

Compositions for intranasal administration include aqueous compositions administered to the nose by drops or by pressurised pump. Suitable compositions contain water as the diluent or carrier for this purpose. Compositions for administration to the lung or nose may contain one or more excipients, for example one or more suspending agents, one or more preservatives, one or more surfactants, one or more tonicity adjusting agents, one or more co-solvents, and may include components to control the pH of the composition, for example a buffer system. Further, the compositions may contain other excipients such as antioxidants, for example sodium metabisulphite, and taste-masking agents. Compositions may also be administered to the nose or other regions of the respiratory tract by nebulisation.

Intranasal compositions may permit the compound(s) of formula (I) or (a) pharmaceutically acceptable salt(s) thereof to be delivered to all areas of the nasal cavities (the target tissue) and further, may permit the compound(s) of formula (I) or (a) pharmaceutically acceptable salt(s) thereof to remain in contact with the target tissue for longer periods of time. A suitable dosing regime for intranasal compositions would be for the patient to inhale slowly through the nose subsequent to the nasal cavity being cleared. During inhalation the composition would be administered to one nostril while the other is manually compressed. This procedure would then be repeated for the other nostril. Typically, one or two sprays per nostril would be administered by the above procedure one, two, or three times each day, ideally once daily. Of particular interest are intranasal compositions suitable for once-daily administration.

The suspending agent(s), if included, will typically be present in an amount of from 0.1 to 5% (w/w), such as from 1.5% to 2.4% (w/w), based on the total weight of the composition. Examples of pharmaceutically acceptable suspending agents include, but are not limited to, Avicel® (microcrystalline cellulose and carboxymethylcellulose sodium), carboxymethylcellulose sodium, veegum, tragacanth, bentonite, methylcellulose, xanthan gum, carbopol and polyethylene glycols.

Compositions for administration to the lung or nose may contain one or more excipients may be protected from microbial or fungal contamination and growth by inclusion of one or more preservatives. Examples of pharmaceutically acceptable anti-microbial agents or preservatives include, but are not limited to, quaternary ammonium compounds (for example benzalkonium chloride, benzethonium chloride, cetrimide, cetylpyridinium chloride, lauralkonium chloride and myristyl picolinium chloride), mercurial agents (for example phenylmercuric nitrate, phenylmercuric acetate and thimerosal), alcoholic agents (for example chlorobutanol, phenylethyl alcohol and benzyl alcohol), antibacterial esters (for example esters of para-hydroxybenzoic acid), chelating agents such as disodium edetate (EDTA) and other anti-microbial agents such as chlorhexidine, chlorocresol, sorbic acid and its salts (such as potassium sorbate) and polymyxin. Examples of pharmaceutically acceptable anti-fungal agents or preservatives include, but are not limited to, sodium benzoate, sorbic acid, sodium propionate, methylparaben, ethylparaben, propylparaben and butylparaben. The preservative(s), if included, may be present in an amount of from 0.001 to 1% (w/w), such as from 0.015% to 0.5% (w/w) based on the total weight of the composition.

Compositions (for example wherein at least one compound is in suspension) may include one or more surfactants which functions to facilitate dissolution of the medicament particles in the aqueous phase of the composition. For example, the amount of surfactant used is an amount which will not cause foaming during mixing. Examples of pharmaceutically acceptable surfactants include fatty alcohols, esters and ethers, such as polyoxyethylene (20) sorbitan monooleate (Polysorbate 80), macrogol ethers, and poloxamers. The surfactant may be present in an amount of between about 0.01 to 10% (w/w), such as from 0.01 to 0.75% (w/w), for example about 0.5% (w/w), based on the total weight of the composition.

One or more tonicity-adjusting agent(s) may be included to achieve tonicity with body fluids e.g. fluids of the nasal cavity, resulting in reduced levels of irritancy. Examples of pharmaceutically acceptable tonicity-adjusting agents include, but are not limited to, sodium chloride, dextrose, xylitol, calcium chloride, glucose, glycerine and sorbitol. A tonicity-adjusting agent, if present, may be included in an amount of from 0.1 to 10% (w/w), such as from 4.5 to 5.5% (w/w), for example about 5.0% (w/w), based on the total weight of the composition.

The compositions of the invention may be buffered by the addition of suitable buffering agents such as sodium citrate, citric acid, trometamol, phosphates such as disodium phosphate (for example the dodecahydrate, heptahydrate, dihydrate and anhydrous forms), or sodium phosphate and mixtures thereof.

A buffering agent, if present, may be included in an amount of from 0.1 to 5% (w/w), for example 1 to 3% (w/w) based on the total weight of the composition.

Examples of taste-masking agents include sucralose, sucrose, saccharin or a salt thereof, fructose, dextrose, glycerol, corn syrup, aspartame, acesulfame-K, xylitol, sorbitol, erythritol, ammonium glycyrrhizinate, thaumatin, neotame, mannitol, menthol, eucalyptus oil, camphor, a natural flavouring agent, an artificial flavouring agent, and combinations thereof.

One or more co-solvent(s) may be included to aid solubility of the medicament compound(s) and/or other excipients. Examples of pharmaceutically acceptable co-solvents include, but are not limited to, propylene glycol, dipropylene glycol, ethylene glycol, glycerol, ethanol, polyethylene glycols (for example PEG300 or PEG400), and methanol. In one embodiment, the co-solvent is propylene glycol.

Co-solvent(s), if present, may be included in an amount of from 0.05 to 30% (w/w), such as from 1 to 25% (w/w), for example from 1 to 10% (w/w) based on the total weight of the composition.

Compositions for inhaled administration include aqueous, organic or aqueous/organic mixtures, dry powder or crystalline compositions administered to the respiratory tract by pressurised pump or inhaler, for example, reservoir dry powder inhalers, unit-dose dry powder inhalers, pre-metered multi-dose dry powder inhalers, nasal inhalers or pressurised aerosol inhalers, nebulisers or insufflators. Suitable compositions contain water as the diluent or carrier for this purpose and may be provided with conventional excipients such as buffering agents, tonicity modifying agents and the like. Aqueous compositions may also be administered to the nose and other regions of the respiratory tract by nebulisation. Such compositions may be aqueous solutions or suspensions or aerosols delivered from pressurised packs, such as a metered dose inhaler, with the use of a suitable liquefied propellant.

Compositions for administration topically to the nose (for example, for the treatment of rhinitis) or to the lung, include pressurised aerosol compositions and aqueous compositions delivered to the nasal cavities by pressurised pump. Compositions which are non-pressurised and are suitable for administration topically to the nasal cavity are of particular interest. Suitable compositions contain water as the diluent or carrier for this purpose. Aqueous compositions for administration to the lung or nose may be provided with conventional excipients such as buffering agents, tonicity-modifying agents and the like. Aqueous compositions may also be administered to the nose by nebulisation.

A fluid dispenser may typically be used to deliver a fluid composition to the nasal cavities. The fluid composition may be aqueous or non-aqueous, but typically aqueous. The compound of formula (I), or a pharmaceutically acceptable salt thereof, may be formulated as a suspension or solution. Such a fluid dispenser may have a dispensing nozzle or dispensing orifice through which a metered dose of the fluid composition is dispensed upon the application of a user-applied force to a pump mechanism of the fluid dispenser. Such fluid dispensers are generally provided with a reservoir of multiple metered doses of the fluid composition, the doses being dispensable upon sequential pump actuations. Alternatively, the fluid dispenser for delivery of a fluid composition to the nasal cavities may be designed to be dose-limited, for example a single use dispenser comprising a single dose. The dispensing nozzle or orifice may be configured for insertion into the nostrils of the user for spray dispensing of the fluid composition into the nasal cavity. A fluid dispenser of the aforementioned type is described and illustrated in International Patent Application publication number WO 2005/044354 (Glaxo Group Limited). The dispenser has a housing which houses a fluid-discharge device having a compression pump mounted on a container for containing a fluid composition. The housing has at least one finger-operable side lever which is movable inwardly with respect to the housing to move the container upwardly in the housing by means of a cam to cause the pump to compress and pump a metered dose of the composition out of a pump stem through a nasal nozzle of the housing. In one embodiment, the fluid dispenser is of the general type illustrated in FIGS. 30-40 of WO 2005/044354.

Aqueous compositions containing a compound of formula (I) or a pharmaceutically acceptable salt thereof may also be delivered by a pump as disclosed in International Patent Application publication number WO2007/138084 (Glaxo Group Limited), for example as disclosed with reference to FIGS. 22-46 thereof, or as disclosed in United Kingdom patent application number GB0723418.0 (Glaxo Group Limited), for example as disclosed with reference to FIGS. 7-32 thereof. The pump may be actuated by an actuator as disclosed in FIGS. 1-6 of GB0723418.0.

Dry powder compositions for topical delivery to the lung by inhalation may, for example, be presented in capsules and cartridges of for example gelatine, or blisters of for example laminated aluminium foil, for use in an inhaler or insufflator. Powder blend compositions generally contain a powder mix for inhalation of the compound of formula (I) or a pharmaceutically acceptable salt thereof and a suitable powder base (carrier/diluent/excipient substance) such as mono-, di-, or polysaccharides (for example lactose or starch). Dry powder compositions may also include, in addition to the drug and carrier, a further excipient (for example a ternary agent such as a sugar ester for example cellobiose octaacetate, calcium stearate, or magnesium stearate.

In one embodiment, a composition suitable for inhaled administration may be incorporated into a plurality of sealed dose containers provided on medicament pack(s) mounted inside a suitable inhalation device. The containers may be rupturable, peelable, or otherwise openable one-at-a-time and the doses of the dry powder composition administered by inhalation on a mouthpiece of the inhalation device, as known in the art. The medicament pack may take a number of different forms, for instance a disk-shape or an elongate strip. Representative inhalation devices are the DISKHALER™ and DISKUS™ devices, marketed by GlaxoSmithKline.

A dry powder inhalable composition may also be provided as a bulk reservoir in an inhalation device, the device then being provided with a metering mechanism for metering a dose of the composition from the reservoir to an inhalation channel where the metered dose is able to be inhaled by a patient inhaling at a mouthpiece of the device. Exemplary marketed devices of this type are TURBUHALER™ (AstraZeneca), TWISTHALER™ (Schering) and CLICKHALER™ (Innovata.)

A further delivery method for a dry powder inhalable composition is for metered doses of the composition to be provided in capsules (one dose per capsule) which are then loaded into an inhalation device, typically by the patient on demand. The device has means to rupture, pierce or otherwise open the capsule so that the dose is able to be entrained into the patient's lung when they inhale at the device mouthpiece. As marketed examples of such devices there may be mentioned ROTAHALER™ (GlaxoSmithKline) and HANDIHALER™ (Boehringer Ingelheim.)

Pressurised aerosol compositions suitable for inhalation can be either a suspension or a solution and may contain a compound of formula (I) or a pharmaceutically acceptable salt thereof and a suitable propellant such as a fluorocarbon or hydrogen-containing chlorofluorocarbon or mixtures thereof, particularly hydrofluoroalkanes, especially 1,1,1,2-tetrafluoroethane, 1,1,1,2,3,3,3-heptafluoro-n-propane or a mixture thereof. The aerosol composition may optionally contain additional composition excipients well known in the art such as surfactants e.g. oleic acid, lecithin or an oligolactic acid or derivative thereof e.g. as described in WO 94/21229 and WO 98/34596 (Minnesota Mining and Manufacturing Company) and co-solvents e.g. ethanol. Pressurised compositions will generally be retained in a canister (e.g. an aluminium canister) closed with a valve (e.g. a metering valve) and fitted into an actuator provided with a mouthpiece.

Ointments, creams and gels, may, for example, be formulated with an aqueous or oily base with the addition of suitable thickening and/or gelling agent and/or solvents. Such bases may thus, for example, include water and/or an oil such as liquid paraffin or a vegetable oil such as arachis oil or castor oil, or a solvent such as polyethylene glycol. Thickening agents and gelling agents which may be used according to the nature of the base include soft paraffin, aluminium stearate, cetostearyl alcohol, polyethylene glycols, wool-fat, beeswax, carboxypolymethylene and cellulose derivatives, and/or glyceryl monostearate and/or non-ionic emulsifying agents.

Lotions may be formulated with an aqueous or oily base and will in general also contain one or more emulsifying agents, stabilising agents, dispersing agents, suspending agents or thickening agents.

Powders for external application may be formed with the aid of any suitable powder base, for example, talc, lactose or starch. Drops may be formulated with an aqueous or non-aqueous base also comprising one or more dispersing agents, solubilising agents, suspending agents or preservatives.

The compounds of formula (I) and pharmaceutically acceptable salts thereof may, for example, be formulated for transdermal delivery by composition into patches or other devices (e.g. pressurised gas devices) which deliver the active component into the skin.

For buccal administration the compositions may take the form of tablets or lozenges formulated in the conventional manner.

The compounds of formula (I) and pharmaceutically acceptable salts thereof may also be formulated as suppositories, e.g. containing conventional suppository bases such as cocoa butter or other glycerides.

The compounds of formula (I) and pharmaceutically acceptable salts thereof may also be formulated for parenteral administration by bolus injection or continuous infusion and may be presented in unit dose form, for instance as ampoules, vials, small volume infusions or pre-filled syringes, or in multidose containers with an added preservative. The compositions may take such forms as solutions, suspensions, or emulsions in aqueous or non-aqueous vehicles, and may contain formulatory agents such as anti-oxidants, buffers, antimicrobial agents and/or tonicity adjusting agents. Alternatively, the active ingredient may be in powder form for constitution with a suitable vehicle, e.g. sterile, pyrogen-free water, before use. The dry solid presentation may be prepared by filling a sterile powder aseptically into individual sterile containers or by filling a sterile solution aseptically into each container and freeze-drying.

The compounds of formula (I) and pharmaceutically acceptable salts thereof may also be formulated with vaccines as adjuvants to modulate their activity. Such compositions may contain antibody(ies) or antibody fragment(s) or an antigenic component including but not limited to protein, DNA, live or dead bacteria and/or viruses or virus-like particles, together with one or more components with adjuvant activity including but not limited to aluminium salts, oil and water emulsions, heat shock proteins, lipid A preparations and derivatives, glycolipids, other TLR agonists such as CpG DNA or similar agents, cytokines such as GM-CSF or IL-12 or similar agents.

In a further aspect of the invention, there is provided a vaccine adjuvant comprising a compound of formula (I), or a pharmaceutically acceptable salt thereof.

There is further provided a vaccine composition comprising a compound of formula (I), or a pharmaceutically acceptable salt thereof, and an antigen or antigen composition.

The compounds of formula (I) and pharmaceutically acceptable salts thereof may be employed alone or in combination with other therapeutically-active agents. The invention provides in a further aspect, a combination comprising a compound of formula (I), or a pharmaceutically acceptable salt thereof, together with at least one other therapeutically-active agent.

The compounds of formula (I) and pharmaceutically acceptable salts thereof and the other therapeutically-active agent(s) may be administered together or separately and, when administered separately, administration may occur simultaneously or sequentially, in any order. The amounts of the compound(s) of formula (I) or (a) pharmaceutically acceptable salt(s) thereof and the other therapeutically-active agent(s) and the relative timings of administration will be selected in order to achieve the desired combined therapeutic effect. The administration of a combination of a compound of formula (I) or a pharmaceutically acceptable salt thereof with other treatment agents may be by administration concomitantly in a unitary pharmaceutical composition including both compounds, or in separate pharmaceutical compositions each including one of the compounds. Alternatively, the combination may be administered separately in a sequential manner wherein one treatment agent is administered first and the other second or vice versa. Such sequential administration may be close in time or remote in time.

The compounds of formula (I) and pharmaceutically acceptable salts thereof may be used in combination with one or more agents useful in the prevention or treatment of viral infections. Examples of such agents include, without limitation; polymerase inhibitors such as those disclosed in WO 2004/037818-A1, as well as those disclosed in WO 2004/037818 and WO 2006/045613; JTK-003, JTK-019, NM-283, HCV-796, R-803, R1728, R1626, as well as those disclosed in WO 2006/018725, WO 2004/074270, WO 2003/095441, US2005/0176701, WO 2006/020082, WO 2005/080388, WO 2004/064925, WO 2004/065367, WO 2003/007945, WO 02/04425, WO 2005/014543, WO 2003/000254, EP 1065213, WO 01/47883, WO 2002/057287, WO 2002/057245 and similar agents; replication inhibitors such as acyclovir, famciclovir, ganciclovir, cidofovir, lamivudine and similar agents; protease inhibitors such as the HIV protease inhibitors saquinavir, ritonavir, indinavir, nelfinavir, amprenavir, fosamprenavir, brecanavir, atazanavir, tipranavir, palinavir, lasinavir, and the HCV protease inhibitors BILN2061, VX-950, SCH503034; and similar agents; nucleoside and nucleotide reverse transcriptase inhibitors such as zidovudine, didanosine, lamivudine, zalcitabine, abacavir, stavidine, adefovir, adefovir dipivoxil, fozivudine, todoxil, emtricitabine, alovudine, amdoxovir, elvucitabine, and similar agents; non-nucleoside reverse transcriptase inhibitors (including an agent having anti-oxidation activity such as immunocal, oltipraz etc.) such as nevirapine, delavirdine, efavirenz, loviride, immunocal, oltipraz, capravirine, TMC-278, TMC-125, etravirine, and similar agents; entry inhibitors such as enfuvirtide (T-20), T-1249, PRO-542, PRO-140, TNX-355, BMS-806, 5-Helix and similar agents; integrase inhibitors such as L-870,180 and similar agents; budding inhibitors such as PA-344 and PA-457, and similar agents; chemokine receptor inhibitors such as vicriviroc (Sch-C), Sch-D, TAK779, maraviroc (UK-427,857), TAK449, as well as those disclosed in WO 02/74769, WO 2004/054974, WO 2004/055012, WO 2004/055010, WO 2004/055016, WO 2004/055011, and WO 2004/054581, and similar agents; neuraminidase inhibitors such as CS-8958, zanamivir, oseltamivir, peramivir and similar agents; ion channel blockers such as amantadine or rimantadine and similar agents; and interfering RNA and antisense oligonucleotides and such as ISIS-14803 and similar agents; antiviral agents of undetermined mechanism of action, for example those disclosed in WO 2005/105761, WO 2003/085375, WO 2006/122011, ribavirin, and similar agents. The compounds of formula (I) and pharmaceutically acceptable salts thereof may also be used in combination with one or more other agents which may be useful in the prevention or treatment of viral infections for example immune therapies (e.g. interferon or other cytokines/chemokines, cytokine/chemokine receptor modulators, cytokine agonists or antagonists and similar agents); and therapeutic vaccines, antifibrotic agents, anti-inflammatory agents such as corticosteroids or NSAIDs (non-steroidal anti-inflammatory agents) and similar agents.

The compounds of formula (I) and pharmaceutically acceptable salts thereof may be used in combination with one or more other agents which may be useful in the prevention or treatment of allergic disease, inflammatory disease, autoimmune disease, for example; antigen immunotherapy, anti-histamines, steroids, NSAIDs, bronchodilators (e.g. beta 2 agonists, adrenergic agonists, anticholinergic agents, theophylline), methotrexate, leukotriene modulators and similar agents; monoclonal antibody therapy such as anti-IgE, anti-TNF, anti-IL-5, anti-IL-6, anti-IL-12, anti-IL-1 and similar agents; receptor therapies e.g. entanercept and similar agents; antigen non-specific immunotherapies (e.g. interferon or other cytokines/chemokines, cytokine/chemokine receptor modulators, cytokine agonists or antagonists, TLR agonists and similar agents).

The compounds of formula (I) and pharmaceutically acceptable salts thereof may be used in combination with one or more other agents which may be useful in the prevention or treatment of cancer, for example chemotherapeutics such as alkylating agents, topoisomerase inhibitors, antimetabolites, antimitotic agents, kinase inhibitors and similar agents; monoclonal antibody therapy such as trastuzumab, gemtuzumab and other similar agents; and hormone therapy such as tamoxifen, goserelin and similar agents.

The pharmaceutical compositions according to the invention may also be used alone or in combination with at least one other therapeutic agent in other therapeutic areas, for example gastrointestinal disease. The compositions according to the invention may also be used in combination with gene replacement therapy.

The invention includes in a further aspect a combination comprising a compound of formula (I), or a pharmaceutically acceptable salt thereof, together with at least one other therapeutically active agent.

The combinations referred to above may conveniently be presented for use in the form of a pharmaceutical composition and thus pharmaceutical compositions comprising a combination as defined above together with at least one pharmaceutically acceptable diluent or carrier thereof represent a further aspect of the invention.

A therapeutically effective amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof will depend upon a number of factors. For example, the species, age, and weight of the recipient, the precise condition requiring treatment and its severity, the nature of the composition, and the route of administration are all factors to be considered. The therapeutically effective amount ultimately should be at the discretion of the attendant physician. Regardless, an effective amount of a compound of the present invention for the treatment of humans suffering from frailty, generally, should be in the range of 0.0001 to 100 mg/kg body weight of recipient per day. More usually the effective amount should be in the range of 0.001 to 10 mg/kg body weight per day. Thus, for a 70 kg adult one example of an actual amount per day would usually be from 7 to 700 mg. For intranasal and inhaled routes of administration, typical doses for a 70 kg adult should be in the range of 0.1 micrograms to 1 mg per day, for example 1 μg, 10 μg or 100 μg. This amount may be given in a single dose per day or in a number (such as two, three, four, five, or more) of sub-doses per day such that the total daily dose is the same. An effective amount of a pharmaceutically acceptable salt of a compound of formula (I) may be determined as a proportion of the effective amount of the compound of formula (I) or a pharmaceutically acceptable salt thereof per se. Similar dosages should be appropriate for treatment of the other conditions referred to herein.

Compounds of formula (I) and pharmaceutically acceptable salts thereof may also be administered at any appropriate frequency e.g. 1-7 times per week. The precise dosing regimen will of course depend on factors such as the therapeutic indication, the age and condition of the patient, and the particular route of administration chosen. In one aspect of the invention, a compound of formula (I), or a pharmaceutically acceptable salt thereof, may be administered once weekly for a period of 4 to 8 weeks, for example 4, 5, 6, 7 or 8 weeks.

Pharmaceutical compositions may be presented in unit-dose forms containing a predetermined amount of active ingredient per unit dose. Such a unit may contain, as a non-limiting example, 0.5 mg to 1 g of a compound of formula (I) or a pharmaceutically acceptable salt thereof, depending on the condition being treated, the route of administration, and the age, weight, and condition of the patient. Preferred unit-dosage compositions are those containing a daily dose or sub-dose, as herein above recited, or an appropriate fraction thereof, of an active ingredient. Such pharmaceutical compositions may be prepared by any of the methods well-known in the pharmacy art.

There is also provided a process for preparing such a pharmaceutical composition which comprises admixing a compound of formula (I), or a pharmaceutically acceptable salt thereof, with one or more pharmaceutically acceptable excipients.

Aspects of the invention are illustrated by reference to, but are in no way limited by, the following Examples.

EXAMPLES Analytical Methodology ¹H NMR

¹H NMR spectra were recorded in either CDCl₃ or DMSO-d₆ on either a Bruker DPX 400 or Bruker Avance DRX, Varian Unity 400 spectrometer or JEOL Delta all working at 400 MHz. The internal standard used was either tetramethylsilane or the residual protonated solvent at 7.25 ppm for CDCl₃ or 2.50 ppm for DMSO-d₆.

LCMS System A

Column: 50 mm×2.1 mm ID, 1.7 m Acquity UPLC BEH C₁₈

Flow Rate: 1 mL/min.

Temp: 40° C.

UV detection range: 210 to 350 nm

Mass spectrum: Recorded on a mass spectrometer using alternative-scan positive and negative mode electrospray ionisation

Solvents:

-   -   A: 0.1% v/v formic acid in water     -   B: 0.1% v/v formic acid acetonitrile

Gradient:

Time (min.) A % B % 0 97 3 1.5 0 100 1.9 0 100 2.0 97 3

System B

Column: 50 mm×2.1 mm ID, 1.7 m Acquity UPLC BEH C₁₈

Flow Rate: 1 mL/min.

Temp: 40° C.

UV detection range: 210 to 350 nm

Mass spectrum: Recorded on a mass spectrometer using alternative-scan positive and negative mode electrospray ionisation

Solvents:

-   -   A: 10 mM ammonium bicarbonate in water adjusted to pH10 with         ammonia solution     -   B: acetonitrile

Gradient:

Time (min.) A % B % 0 99 1 1.5 3 97 1.9 3 97 2.0 99 1

Mass Directed Autopreparative HPLC (MDAP)

Mass directed autopreparative HPLC was undertaken under the conditions given below. The UV detection was an averaged signal from wavelength of 210 nm to 350 nm and mass spectra were recorded on a mass spectrometer using alternate-scan positive and negative mode electrospray ionization.

Method A

Method A was conducted on a Sunfire C₁₈ column (typically 150 mm×30 mm i.d. 5 μm packing diameter) at ambient temperature. The solvents employed were:

A=0.1% v/v solution of formic acid in water

B=0.1% v/v solution of formic acid in acetonitrile.

Method B

Method B was conducted on an XBridge C₁₈ column (typically 100 mm×30 mm i.d. 5 μm packing diameter) at ambient temperature. The solvents employed were:

A=10 mM aqueous ammonium bicarbonate adjusted to pH 10 with ammonia solution.

B=acetonitrile.

Abbreviations

The following list provides definitions of certain abbreviations as used herein. It will be appreciated that the list is not exhaustive, but the meaning of those abbreviations not herein below defined will be readily apparent to those skilled in the art.

-   DCM Dichloromethane -   DMF N, N-Dimethylformamide -   DMSO Dimethylsulphoxide -   THF Tetrahydrofuran -   EtOAc Ethyl acetate -   MeOH Methanol -   EtOH Ethanol -   MeCN Acetonitrile -   HCl Hydrochloric acid -   HPLC High performance liquid chromatography -   MDAP Mass Directed Autopreparative HPLC -   SPE Solid phase extraction -   MeOH Methanol -   TBME tert-Butyl methy ether -   TFA Trifluoroacetic acid -   DIPEA N, N-Diisopropylethylamine

Reaction Intermediates Intermediate 1: Ethyl 3-acetimidamido-5-methyl-1H-pyrrole-2-carboxylate

To a suspension of ethyl 3-amino-5-methyl-1H-pyrrole-2-carboxylate (10.876 g, 64.7 mmol) in acetonitrile (200 mL) was added 4M HCl in dioxane (81 mL, 323 mmol). This was heated at 60° C. under a nitrogen atmosphere for 4 days. The reaction mixture was filtered to give the title compound as an off white solid (12.738 g).

LCMS (System B): t_(RET)=0.45, 0.47 min; MH⁺ 210

Intermediate 2: 2,6-Dimethyl-3H-pyrrolo[3,2-d]pyrimidin-4(5H)-one

To a suspension of ethyl 3-acetimidamido-5-methyl-1H-pyrrole-2-carboxylate, hydrochloride (12.7 g, 51.7 mmol) in ethanol (200 mL) was added 5M NaOH (41.4 mL, 207 mmol) in one charge. This was put under a nitrogen atmosphere and was heated to 90° C. for 2 hours. The reaction mixture was concentrated in vacuo and to this was added an aqueous solution of 5% citric acid (200 mL) until the pH was neutralised. A solid appeared at pH 7, it was filtrated and washed with water to give the title compound as a pale brown solid (6.806 g).

LCMS (System B): t_(RET)=0.45 min; MH⁺ 164

The filtrate was concentrated in vacuo and filtered to afford a further batch of the title compound (0.5 g).

LCMS (System B): t_(RET)=0.45 min; MH⁺ 164

Intermediate 3: 4-Chloro-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidine

In a round bottomed flask was introduced 2,6-dimethyl-3H-pyrrolo[3,2-d]pyrimidin-4(5H)-one (6.15 g, 37.7 mmol) and this was dissolved in POCl₃ (70.3 ml, 754 mmol). The reaction mixture was then heated to 90° C. for 30 hours. The reaction mixture was evaporated in vacuo to give a brown oil. This was dissolved in toluene and evaporated again to remove the remaining POCl₃ in the mixture. The residue was then diluted in water (50 mL) and sodium bicarbonate was added to it until the pH reached 7-8. A white precipitate appeared and was filtered and then washed with water. This was dried for 2 hours to give the title compound (5.617 g) as a white solid.

LCMS (System B): t_(RET)=0.59 min; MH⁺ 182/184

The filtrate was concentrated in vacuo, filtered, washed and dried to afford a further batch of the title compound (0.22 g).

LCMS (System B): t_(RET)=0.59 min; MH⁺ 182/184

Intermediate 4: 4-Chloro-7-iodo-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidine

To a stirred solution of 4-chloro-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidine (6.68 g, 36.8 mmol) in tetrahydrofuran (100 mL) under nitrogen at room temperature was added N-iodosuccinimide (9.52 g, 42.3 mmol) portionwise. The reaction mixture was stirred at room temperature under nitrogen for 1 hour. The reaction mixture was then diluted with TBME. This was washed with sodium thiosulfate solution (150 mL) and brine. The organic layer was then passed through a hydrophobic frit and concentrated in vacuo. The sample was preabsorbed on florosil and purified on silica (750 g) using a gradient of 0-100% TBME-cyclohexane over 11 column volumes. The appropriate fractions were combined and evaporated in vacuo to give the title compound as a yellow solid (9.854 g).

LCMS (System A): t_(RET)=0.75 min; MH⁺ 308/310

Intermediate 5: 5-((Benzyloxy)methyl)-4-chloro-7-iodo-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidine

To a solution of 4-chloro-7-iodo-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidine (1.098 g, 3.57 mmol) in N,N-dimethylformamide (25 mL) cooled with an ice bath was added sodium hydride (0.286 g, 7.14 mmol) portionwise during 5 minutes. The reaction mixture was stirred during 30 minutes before adding benzyl chloromethyl ether (0.891 mL, 6.43 mmol). The reaction mixture was stirred at room temperature under a nitrogen atmosphere during 1 hour. The reaction mixture was quenched with water (50 mL) and partitioned between ethyl acetate (200 mL) and water (200 mL). The organic layer was washed with water and brine (200 mL) and passed through a hydrophobic frit before being concentrated in vacuo. The sample was dissolved in dichloromethane and purified on a silica cartridge (70 g) using a gradient of 0-25% ethyl acetate-cyclohexane over 40 minutes. The appropriate fractions were combined and evaporated in vacuo to give the title compound as a white solid (1.4 g).

LCMS (System A): t_(RET)=1.18 min; MH⁺ 428/430

Intermediate 6: 5-((Benzyloxy)methyl)-7-iodo-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine

5-((Benzyloxy)methyl)-4-chloro-7-iodo-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidine (3.458 g) was split in three 20 mL microwave vials. To each microwave vial was added 1.15 g of the starting material and this was diluted with IPA (10 mL) before 0.88 ammonia (2.5 mL) was added to each. The vials were sealed and heated in the microwave (Biotage) at 150° C. (High Power) for 5 hours. Monitoring by LCMS showed that the reaction went to completion in two of the three microwave sealed vials: additional 0.88 ammonia (2.5 mL) was added to the vial containing unreacted starting material and the mixture heated in the microwave for another 5 hours. The reaction mixture of the three vials were combined and the vials were washed with IPA. This was then concentrated in vacuo to give an orange oil which was triturated with TBME (15 mL) to give the title compound as a yellow solid (2.352 g).

LCMS (System A): t_(RET)=0.69 min; MH⁺ 409

The filtrate was concentrated in vacuo and re-triturated with TBME (10 mL) to give a second batch of the title compound as a yellow solid (267 mg).

LCMS (System A): t_(RET)=0.67 min; MH⁺ 409

Intermediate 7: 1-(Hex-5-yn-1-yl)piperidine

A solution of 6-chlorohex-1-yne (5 mL, 41.3 mmol), piperidine (4.08 mL, 41.3 mmol) and sodium hydrogen carbonate (4.16 g, 49.5 mmol) in DMF (50 mL) was refluxed for 16 hr. The reaction was concentrated in vacuo and the residue partitioned between ether (150 mL) and water (150 mL). The organic was separated and the aqueous back extracted with diethyl ether (50 mL). The combined organics were washed with brine (150 mL), dried (MgSO₄), filtered and concentrated in vacuo to give a crude sample of the title compound (3.74 g). Oxalic acid (2.161 g, 24 mmol) was added to the crude product. The resultant solid was recrystallised from ethanol, collected by filtration and dried in vacuo to give 1-(hex-5-yn-1-yl)piperidine oxalic acid salt (4.66 g). The solid was partitioned between diethyl ether (150 mL) and saturated aqueous sodium bicarbonate (150 mL). The organic was separated and dried (MgSO₄) filtered and concentrated in vacuo to give the title compound as a yellow oil (1.93 g).

¹H NMR (400 MHz, CDCl₃) δ ppm 2.31-2.52 (m, 6H) 2.18-2.26 (m, 2H) 1.92-1.96 (m, 1H) 1.40-1.72 (m, 10H)

Intermediate 8: 5-((Benzyloxy)methyl)-2,6-dimethyl-7-(6-(piperidin-1-yl)hex-1-yn-1-yl)-5H-pyrrolo[3,2-d]pyrimidin-4-amine

To a stirred degassed suspension of 5-((benzyloxy)methyl)-7-iodo-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine (407 mg, 0.997 mmol), copper (I) iodide (27.5 mg, 0.145 mmol) and bis(triphenylphosphine)palladium(II)dichloride (49.0 mg, 0.070 mmol) was added triethylamine (0.221 mL, 1.595 mmol) in anhydrous DMF (8 mL). The solution was left to stir for 30 minutes then a solution of 1-(5-hexyn-1-yl)piperidine (247 mg, 1.495 mmol) in DMF (2 mL) was added dropwise over 5 minutes. The reaction was stirred at 55° C. for 2 hours followed by 60° C. for 1 hour. Another portion of 1-(5-hexyn-1-yl)piperidine (247 mg, 1.495 mmol) was added and the reaction was left to stir for 1.5 hours at 60° C. then allowed to stir at room temperature overnight. The reaction was concentrated in vacuo to give a brown oil. The oil was partitioned between DCM (100 mL) and water (100 mL), The organic phase was separated and the aqueous phase back extracted with DCM (100 mL). The combined organic extracts were dried using a hydrophobic frit and concentrated in vacuo to yield a dark orange oil (902 mg). The crude material was dissolved in dichloromethane and purified on a silica cartridge (100 g) using a 0-25% methanol-dichloromethane gradient over 60 minutes. The appropriate fractions were combined and evaporated in vacuo to give the title compound as two batches.

Batch 1 a clear oil (42 mg)

LCMS (System B): t_(RET)=1.08 min; MH⁺ 446

Batch 2 a pale yellow solid (117 mg)

LCMS (System B): t_(RET)=1.11 min; MH⁺ 446

Intermediate 9: 5-((Benzyloxy)methyl)-7-(5-chloropent-1-yn-1-yl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine

To a nitrogen degassed solution of 5-((benzyloxy)methyl)-7-iodo-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine (300 mg, 0.735 mmol) in anhydrous N,N-dimethylformamide (7 mL) under nitrogen atmosphere at room temperature was added copper(I) iodide (30.8 mg, 0.162 mmol), bis(triphenylphosphine)palladium(II)dichloride (61.9 mg, 0.088 mmol) and finally triethylamine (0.205 mL, 1.470 mmol). The mixture was stirred at room temperature under nitrogen atmosphere for 10 minutes and then a solution of 5-chloropent-1-yne (151 mg, 1.470 mmol) in anhydrous N,N-dimethylformamide (5 mL) was added. The reaction mixture was stirred at 60° C. for 2 h. The reaction was evaporated in vacuo to yield a brown oil. The oil was partitioned between water/brine (1:1) (100 mL) and DCM (100 mL). The organic layer was separated, passed through a hydrophobic frit and evaporated in vacuo to yield a dark orange oil (538 mg). The material was dissolved in 50:50 DMSO/MeOH (6×1 ml) and purified by MDAP (Method B). Appropriate fractions were combined and evaporated in vacuo to yield the title compound as a pale yellow solid (132 mg).

LCMS (System B): t_(RET)=1.10 min; MH⁺ 383

Intermediate 10: 5-((Benzyloxy)methyl)-7-(6-chlorohex-1-yn-1-yl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine

To a nitrogen degassed solution of 5-((benzyloxy)methyl)-7-iodo-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine (482.7 mg, 1.182 mmol) in anhydrous N,N-dimethylformamide (7 mL) under nitrogen atmosphere at room temperature was added copper(I) iodide (49.5 mg, 0.260 mmol), bis(triphenylphosphine)palladium(II)dichloride (100 mg, 0.142 mmol) and finally triethylamine (0.330 mL, 2.365 mmol). The mixture was stirred at room temperature under nitrogen atmosphere for 10 minutes and then a solution of 6-chlorohex-1-yne (276 mg, 2.365 mmol) in anhydrous N,N-dimethylformamide (1 mL) was added. The reaction mixture was stirred at 65° C. for 15 hours then the reaction mixture was concentrated in vacuo. The crude product was dissolved in DMSO and purified by reverse phase column chromatography (120 g C18 column) using a gradient of 35 to 90% acetonitrile+0.1% ammonia/10 mM ammonium bicarbonate in water adjusted to pH10 with ammonia solution over 12 column volumes. Appropriate fractions were combined and evaporated in vacuo to yield the title compound as a pale yellow solid (215 mg).

LCMS (System B): t_(RET)=1.15 min; MH⁺ 397

Example Preparation Example 1 2,6-Dimethyl-7-(6-(piperidin-1-yl)hexyl)-5H-pyrrolo[3,2-d]pyrimidin-4-amine

A filtered solution of 5-((benzyloxy)methyl)-2,6-dimethyl-7-(6-(piperidin-1-yl)hex-1-yn-1-yl)-5H-pyrrolo[3,2-d]pyrimidin-4-amine (159 mg, 0.357 mmol) in ethanol (15 mL) and acetic acid (1.5 mL) was hydrogenated using the H-cube (settings: 60° C., Full H₂, 1 mL/min flow rate) and a 10% Pd/C CatCart 30 as the catalyst. The solution was re-hydrogenated using the H-cube (settings: 60° C., Full H₂, 1 mL/min flow rate) and the same 10% Pd/C CatCart 30 as the catalyst. The solution was concentrated in vacuo. The solid was dissolved in 50:50 DMSO/MeOH (2×1 mL) and purified by MDAP (Method B). Appropriate fractions were combined and evaporated in vacuo to yield the title compound as a cream solid (62 mg).

LCMS (System B): t_(RET)=0.80 min; MH⁺ 330

Example 2 2,6-Dimethyl-7-(5-(pyrrolidin-1-yl)pentyl)-5H-pyrrolo[3,2-d]pyrimidin-4-amine maleate

To a solution of 5-((benzyloxy)methyl)-7-(5-chloropent-1-yn-1-yl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine (251 mg, 0.656 mmol) in anhydrous acetonitrile (4 mL) was added pyrrolidine (0.164 mL, 1.967 mmol) and triethylamine (0.274 mL, 1.967 mmol). The reaction was stirred at 70° C. for 22 hours. An additional portion of pyrrolidine (1.5 equivalent) and triethylamine (1.5 equivalent) were added and the mixture was left to stir for a further 24 hours. The reaction was concentrated in vacuo to give a brown oil. The oil was partitioned between EtOAc and water. The organic phase was separated and the aqueous phase back extracted with EtOAc. The combined organic extracts were dried using a hydrophobic frit and concentrated in vacuo to yield a brown oil (315 mg). The crude product was dissolved in ethanol (40 mL) and was hydrogenated using the H-cube (settings: 25° C., Full H₂, 1 mL/min flow rate) and a 10% Pd/C CatCart 30 as the catalyst. The solution was concentrated in vacuo to yield a pale yellow oil (275 mg). The material was dissolved in dichloromethane and purified on a silica cartridge (20 g) using a 0-50% methanol-dichloromethane gradient over 40 minutes. Fractions containing the desired product were combined and concentrated in vacuo to yield 174 mg of yellow oil. The material was redissolved in EtOH (25 mL) and acetic acid (2.5 mL) and run through the Hcube (settings: 60° C., Full H₂, 1 mL/min flow rate) and a 10% Pd/C CatCart 30 as the catalyst. The solution was run through the Hcube until the reaction had gone to completion and complete removal of BOM group had occurred (3 times using the same settings). The ethanol solution was evaporated to dryness to yield a clear oil (149 mg). The material was dissolved in 50:50 DMSO/MeOH (2×1 mL) and purified by MDAP (Method B). Appropriate fractions were combined and evaporated in vacuo to yield the free base of the title compound as a white solid (60 mg).

LCMS (System B): t_(RET)=0.65 min; MH⁺ 302

2,6-dimethyl-7-(5-(pyrrolidin-1-yl)pentyl)-5H-pyrrolo[3,2-d]pyrimidin-4-amine (11.3 mg, 0.037 mmol) was dissolved in MeOH/DCM and maleic acid (6.53 mg, 0.056 mmol) was added. The solution was evaporated to dryness to yield the title compound as the maleate salt as a clear oil (16.7 mg)

LCMS (System B): t_(RET)=0.66 min; MH⁺ 302

Example 3 2,2′-((5-(4-Amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)pentyl)azanediyl)diethanol formate

To a stirred solution of 5-((benzyloxy)methyl)-7-(5-chloropent-1-yn-1-yl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine (132 mg, 0.345 mmol) in N,N-dimethylformamide (3 mL) was added triethylamine (0.144 mL, 1.034 mmol) and diethanolamine (109 mg, 1.034 mmol). The resultant mixture was heated at 70° C. for 22 hours. To the reaction mixture was added further diethanolamine (109 mg, 1.034 mmol) and triethylamine (0.144 mL, 1.034 mmol) and heating at 70° C. continued for 48 hours. The reaction mixture was concentrated in vacuo and the residue was dissolved in MeOH (25 mL) and acetic acid (2 mL) was added. The solution was hydrogenated using the H-cube (settings: 60° C., Full H₂, 1 mL/min flow rate) and 10% Pd/C CatCart 30 as the catalyst. The methanol solution was re run through the H-cube using the same settings as above. The methanol solution was evaporated to dryness and the crude material was dissolved in 50:50 DMSO/MeOH (6×1 mL) and purified by MDAP (Method B). Appropriate fractions were combined and evaporated in vacuo to yield the title compound as a white solid (82 mg).

LCMS (System B): t_(RET)=0.59 min; MH⁺ 336

Example 4 2,2′-((6-(4-Amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)azanediyl)diethanol formate

Prepared similarly to Example 3 from 5-((benzyloxy)methyl)-7-(6-chlorohex-1-yn-1-yl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine and diethanolamine.

LCMS (System B): t_(RET)=0.64 min; MH⁺ 350

Example 5 2-((6-(4-Amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)(2-methoxyethyl)amino)ethanol

To a stirred solution of 5-((benzyloxy)methyl)-7-(6-chlorohex-1-yn-1-yl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine (215 mg, 0.542 mmol) in N,N-Dimethylformamide (4 mL) was added triethylamine (0.226 mL, 1.625 mmol) and 2-((2-methoxyethyl)amino)ethanol (0.191 mL, 1.625 mmol). The resultant mixture was heated at 70° C. for 40 hours. To the reaction mixture was added further 2-((2-methoxyethyl)amino)ethanol (0.191 mL, 1.625 mmol) and triethylamine (0.226 mL, 1.625 mmol) and heating at 75° C. continued for 24 hours. The reaction mixture was concentrated in vacuo and the residue was dissolved in MeOH (25 mL) then acetic acid (2 mL) was added. The solution was hydrogenated using the H-cube (settings: 60° C., Full H₂, 1 mL/min flow rate) and 10% Pd/C CatCart 30 as the catalyst.

The solution was re-run through the H-cube 3 more times using the same settings as above. The solvent was evaporated in vacuo. The crude material was dissolved in 50:50 DMSO/MeOH (4×1 mL) and purified by MDAP (Method B). Appropriate fractions were combined and evaporated in vacuo to yield a pale yellow oil (93 mg). The oil was re-purified by MDAP (Method B). Appropriate fractions were combined and evaporated in vacuo to yield the title compound (27 mg).

LCMS (System B): t_(RET)=0.70 min; MH⁺ 364

Example 6 7-(6-(bis(2-Methoxyethyl)amino)hexyl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine

To a stirred solution of 5-((benzyloxy)methyl)-7-(6-chlorohex-1-yn-1-yl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine (315.6 mg, 0.795 mmol) in N,N-dimethylformamide (5 mL) was added triethylamine (0.332 mL, 2.385 mmol) and bis(2-methoxyethyl)-amine (0.349 mL, 2.385 mmol). The resultant mixture was heated at 70° C. for 20 hours. To the reaction mixture was added further bis(2-methoxyethyl)-amine (0.349 mL, 2.385 mmol) and triethylamine (0.332 mL, 2.385 mmol) and heating at 70° C. continued for 32 hours. The reaction mixture was concentrated in vacuo and the residue was dissolved in MeOH (40 mL) and acetic acid (4 mL) was added. The solution was hydrogenated using the H-cube (settings: 65° C., Full H₂, 1 mL/min flow rate) and 10% Pd/C CatCart 30 as the catalyst. The solution was re run through the H-cube 3 more times using the same settings as above and changing the catcart at each run through. The methanol was evaporated in vacuo. The crude material was dissolved in 50:50 DMSO/MeOH (3×1 mL) and purified by MDAP (Method B). Appropriate fractions were combined and evaporated in vacuo to yield the title compound (84.5 mg).

LCMS (System B): t_(RET)=0.82 min; MH⁺ 378

Example 7 2-((6-(4-Amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)amino)ethanol

To a stirred solution of 5-((benzyloxy)methyl)-7-(6-chlorohex-1-yn-1-yl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine (220.6 mg, 0.556 mmol) in acetonitrile (4 mL) was added triethylamine (0.232 mL, 1.667 mmol) and 2-aminoethanol (0.101 mL, 1.667 mmol). The resultant mixture was heated at 70° C. for 21 hours. To the reaction mixture was added further 2-aminoethanol (0.101 mL, 1.667 mmol) and triethylamine (0.232 mL, 1.667 mmol) and heating at 70° C. continued for 46 hours. The reaction mixture was concentrated in vacuo and the residue was dissolved in MeOH (25 mL) and acetic acid (2 mL) was added. The solution was hydrogenated using the H-cube (settings: 60° C., Full H₂, 1 mL/min flow rate) and 10% Pd/C CatCart 30 as the catalyst. The methanol solution was re run through the H-cube twice more using the same settings as above. The methanol was evaporated in vacuo. The crude material was dissolved in 50:50 DMSO/MeOH (5×1 mL) and purified by MDAP (Method B). Appropriate fractions were combined and evaporated in vacuo to yield the title compound as a clear oil (43.7 mg).

LCMS (System B): t_(RET)=0.55 min; MH⁺ 306

Example 8 (3R,5S)-1-(6-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)piperidine-3,5-diol

To a stirred solution of 5-((benzyloxy)methyl)-7-(6-chlorohex-1-yn-1-yl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine (215 mg, 0.542 mmol) in N,N-Dimethylformamide (4 mL) was added triethylamine (0.226 mL, 1.625 mmol) and (3R,5S)-piperidine-3,5-diol (250 mg, 1.625 mmol). The resultant mixture was heated at 70° C. for 16 hours. To the reaction mixture was added further (3R,5S)-piperidine-3,5-diol (250 mg, 1.625 mmol) and triethylamine (0.226 mL, 1.625 mmol) and heating at 75° C. continued for 72 hours. The reaction mixture was concentrated in vacuo and the residue was dissolved in methanol (45 mL) and acetic acid (5 mL) was added. The solution was hydrogenated using the H-cube (settings: 60° C., Full H₂, 1 mL/min flow rate) and 10% Pd/C CatCart 30 as the catalyst. The methanol solution was re run through the H-cube twice more using the same settings as then evaporated in vacuo. The crude material was dissolved in 50:50 DMSO/MeOH (8×1 mL) and purified by MDAP (Method B). Appropriate fractions were combined and evaporated in vacuo to yield the title compound as a cream solid (160.7 mg).

LCMS (System B): t_(RET)=0.60 min; MH⁺ 362

Example 9 (3R,5R)-1-(6-(4-Amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)piperidine-3,5-diol

To a stirred solution of 5-((benzyloxy)methyl)-7-(6-chlorohex-1-yn-1-yl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine (165 mg, 0.416 mmol) in N,N-Dimethylformamide (3 mL) was added triethylamine (0.174 mL, 1.247 mmol) and (3R,5R)-piperidine-3,5-diol (192 mg, 1.247 mmol) (Tetrahedron 67(7), 1485, 2011). The resultant mixture was heated at 70° C. for 32 hours. To the reaction mixture was added further (3R,5R)-piperidine-3,5-diol (192 mg, 1.247 mmol) and further triethylamine (0.174 mL, 1.247 mmol) and heating at 75° C. continued for 5 hours. The reaction mixture was concentrated in vacuo and the residue was dissolved in MeOH (30 mL) and acetic acid (3 mL) was added. The solution was hydrogenated using the H-cube (settings: 60° C., Full H₂, 1 mL/min flow rate) and 10% Pd/C CatCart 30 as the catalyst. The methanol solution was re run through the H-cube twice more using the same settings as above then was evaporated in vacuo. The crude material was dissolved in 50:50 DMSO/MeOH (7×1 mL) and purified by MDAP (Method B). Appropriate fractions were combined and evaporated in vacuo to yield the title compound as a clear oil (95.2 mg).

LCMS (System B): t_(RET)=0.62 min; MH⁺ 362

Example 10 7-(6-(Dimethylamino)hexyl)-2,6-dimethyl-5H-pyrrolo[3,2-]pyrimidin-4-amine

To a stirred solution of 5-((benzyloxy)methyl)-7-(6-chlorohex-1-yn-1-yl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine (183.7 mg, 0.463 mmol) in N,N-dimethylformamide (3 mL) was added triethylamine (0.194 mL, 1.388 mmol) and 2-aminoethanol (0.084 mL, 1.388 mmol). The resultant mixture was heated at 70° C. for 18 hours. The reaction mixture was concentrated in vacuo and the crude material was dissolved in 50:50 DMSO/MeOH (3×1 mL) and purified by MDAP (Method B). Fractions containing desired product were combined and concentrated to yield a pale yellow oil (73 mg). The oil was dissolved in MeOH (20 mL) and hydrogenated using the H-cube (settings: 60° C., Full H2, 1 mL/min flow rate) and 10% Pd/C CatCart 30 as the catalyst. The methanol was evaporated in vacuo and the crude material was dissolved in 50:50 DMSO/MeOH (1 mL) and purified by MDAP (Method B). Appropriate fractions were combined and evaporated in vacuo to yield the title compound as a cream solid (24.2 mg).

LCMS (System B): t_(RET)=0.66 min; MH⁺ 290

Biological Evaluation

Compounds of the invention were tested for in vitro biological activity in accordance with the following assay.

Assay for the Induction of Interferon-α and TNF-α Using Fresh Human Whole Blood (WB) Compound Preparation

Compounds were prepared at 100× required concentration in DMSO in flat-bottom microtitre plates at a volume of 1.5 μL. Columns 1-10 contained a 1 in 4 serial dilution of the test compound. Included on each plate was a serial dilution of the TLR7/8 agonist resiquimod as a standard and Column 11 contained 1.5 μl of 200 μM resiquimod (giving a 2 μM final concentration, used to define the approximate maximal response to resiquimod). Each compound was assayed in duplicate for each donor.

Incubation and Assays for Interferon-α and TNF-α

Blood samples from three human donors were collected into sodium heparin (10 U/ml). 150 μl of whole Blood was dispensed into Col 1 to 11 of assay plates containing 1.5 μl of test compound or standard in DMSO. Plates were placed in an incubator overnight (37° C., 95% air, 5% CO₂). Following the overnight incubation, plates were removed from the incubator & mixed on an orbital shaker for approximately 1 minute. 100 μl of 0.9% saline was added to each well and the plates mixed again on an orbital shaker. Plates were then centrifuged (2500 rpm, 10 mins), after which a sample of plasma was removed using a Biomek FX and assayed for both IFN-α and TNF-α using the MSD (Mesoscale Discovery) electrochemiluminescence assay platform. The IFN-α assay was carried out similarly to that described above. The TNF-α assay was carried out as per kit instructions (Cat No K111BHB).

Cytokine released was expressed as a percentage of the 2 μM resiquimod control (column 11). This percentage was plotted against compound concentration and the pEC₅₀ for the response determined by non-linear least squares curve fitting. For the IFN-α responses, generally a 4 parameter logistic model was selected. For the TNF-α responses where a clear maximum response was obtained (i.e. a well defined plateau in the response was observed) then a 4 parameter model was generally used. If the upper asymptote of the curve wasn't well defined then the curve fitting was generally constrained to a maximal response of 100% (i.e. to the response to 2 μM resiquimod) or to the response of the highest concentration tested if this was greater than the resiquimod response. Some curves were bell shaped for one or both cytokines and the cytokine data on the down slope of the bell shaped response (i.e. concentrations above those giving the maximal response) were generally excluded from the fit, usually with the exception of the concentration immediately above the peak response. Curve fitting thus concentrated on the up slope of the dose response curve.

Results

Examples 1 to 10 had a mean pEC₅₀ for IFN-α≦5.7.

Examples 1 to 10 had a mean pEC₅₀ for TNF-α of ≦4.3.

Assay for the Induction of Interferon-α and TNF-α Using Fresh Human Peripheral Blood Mononuclear Cells (PBMCs) Compound Preparation

Compounds were dispensed by at 100× the required concentration in DMSO (1 uL/well in a flat bottom 96-well cell culture plate). Each compound was assayed in duplicate for each donor. Each plate contained a dilution series of the TLR7/8 agonist resiquimod as standard and Column 11 contained 1 μL of 200 μM resiquimod (giving a 2 μM final concentration, used to define the approximate maximal response to resiquimod).

Preparation of PBMCs

Blood samples from three human donors were collected into sodium heparin (10 U/ml). 25 mL volumes of whole blood were overlaid onto 15 mL Histopaque in Leucosep tubes which were centrifuged at 400 g for 30 min and the band at the plasma/histopaque interface carefully removed into a sterile 50 mL conical tube. The volume in the tube was made up to 50 mL with sterile DPBS (Dulbecco's phosphate buffered saline, —CaCl₂/MgCl₂) and centrifuged at 300 g for 10 min. The cell pellet was resuspended in 20 mL of media (RPMI 1640 (Low endotoxin) supplemented with 10% v/v foetal calf serum (FCS, low endotoxin) 100 U/mL penicillin G, 100 μg/mL streptomycin, 10 mM L-glutamine and 1× non-essential amino acids), and the cells counted using the Nucleoview 3000 (Chemometec, Via-1 Cassette). The PBMCs concentration was adjusted to give a final concentration of 2×10⁶/mL and 100 uL of this cells suspension was added to wells containing 1 μL of diluted test compound.

Incubation and Assays for Interferon-α and TNF-α

The cell preparations were incubated for 24 hr (37° C., 95% air, 5% CO₂) after which a sample of the supernatant was removed using the Biomek FX and assayed for both IFN-α and TNF-α using the MSD (Mesoscale Discovery) electrochemiluminescence assay platform. The IFN-α assay was carried out similarly to that described above. The TNF-α assay was carried out as per kit instructions (Cat No K111BHB).

Cytokine released was expressed as a percentage of the 2 μM resiquimod control (column 11). This percentage was plotted against compound concentration and the pEC50 for the response determined by non-linear least squares curve fitting. For the IFN-α responses generally a 4 parameter logistic model was selected. For the TNF-α responses where a clear maximum response was obtained (i.e. a well defined plateau in the response was observed) then a 4 parameter model was generally used. If the upper asymptote of the curve wasn't well defined then the curve fitting was generally constrained to a maximal response of 100% (i.e. to the response to 2 μM resiquimod) or to the response of the highest concentration tested if this was greater than the resiquimod response. Some curves were bell shaped for one or both cytokines and the cytokine data on the down slope of the bell shaped response (i.e. concentrations above those giving the maximal response) were generally excluded from the fit, usually with the exception of the concentration immediately above the peak response. Curve fitting thus concentrated on the up slope of the dose response curve.

Results

Examples 1 to 9 had mean pEC₅₀ for IFN-α of from 5.4 to 6.3.

Examples 1 to 9 had mean pEC₅₀ for TNF-α≦4.3. 

1. A compound of formula (I), or a salt thereof:

wherein: R¹ is hydrogen, methyl or —(CH₂)₂R³, R² is methyl or —(CH₂)₂OR⁴, or R¹ and R², together with the nitrogen atom to which they are attached, are linked to form a 5- or 6-membered heterocyclyl wherein the 6-membered heterocyclyl is optionally substituted by two hydroxy substituents; R³ and R⁴ are each independently hydrogen or methyl; and n is an integer having a value of 5 or
 6. 2. A compound according to claim 1, or a salt thereof, wherein R¹ is hydrogen, methyl or —(CH₂)₂OR³, and R² is methyl or —(CH₂)₂OR⁴.
 3. A compound according to claim 1 wherein R¹ and R², together with the nitrogen atom to which they are attached, are linked to form a 5- or 6-membered heterocyclyl wherein the 6-membered heterocyclyl is optionally substituted by two hydroxy substituents.
 4. A compound according to claim 1 wherein n is
 5. 5. A compound according to any claim 1 wherein n is
 6. 6. A compound, or a salt thereof, selected from: 2,6-dimethyl-7-(6-(piperidin-1-yl)hexyl)-5H-pyrrolo[3,2-d]pyrimidin-4-amine; 2,6-dimethyl-7-(5-(pyrrolidin-1-yl)pentyl)-5H-pyrrolo[3,2-d]pyrimidin-4-amine; 2,2′-((5-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)pentyl)azanediyl)diethanol; 2,2′-((6-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)azanediyl)diethanol; 2-((6-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)(2-methoxyethyl)amino)ethanol; 7-(6-(bis(2-methoxyethyl)amino)hexyl)-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-4-amine; 2-((6-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)amino)ethanol; (3R,5S)-1-(6-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)piperidine-3,5-diol; (3R,5R)-1-(6-(4-amino-2,6-dimethyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)hexyl)piperidine-3,5-diol; or 7-(6-(dimethylamino)hexyl)-2,6-dimethyl-5H-pyrrolo[3,2-]pyrimidin-4-amine.
 7. A compound according to claim 1, which is in the form of a pharmaceutically acceptable salt.
 8. A compound according to claim 1, which is in the form of a free base.
 9. A pharmaceutical composition comprising a compound as defined in claim 1, or a pharmaceutically acceptable salt thereof, and one or more pharmaceutically acceptable excipients.
 10. A vaccine composition comprising a compound as defined in claim 1, or a pharmaceutically acceptable salt thereof, and an antigen or antigen composition.
 11. (canceled)
 12. (canceled)
 13. (canceled)
 14. A method of treatment of an allergic disease or other inflammatory condition, an infectious disease or cancer, which method comprises administering to a human subject in need thereof, a therapeutically effective amount of a compound as defined in claim 1, or a pharmaceutically acceptable salt thereof.
 15. A method of treatment of allergic rhinitis, which method comprises administering to a human subject in need thereof, a therapeutically effective amount of a compound as defined in claim 1, or a pharmaceutically acceptable salt thereof.
 16. A method of treatment of asthma, which method comprises administering to a human subject in need thereof, a therapeutically effective amount of a compound as defined in claim 1, or a pharmaceutically acceptable salt thereof.
 17. A compound according to claim 6, which is in the form of a pharmaceutically acceptable salt.
 18. A compound according to claim 6, which is in the form of a free base.
 19. A pharmaceutical composition comprising a compound as defined in claim 6, or a pharmaceutically acceptable salt thereof, and one or more pharmaceutically acceptable excipients.
 20. A vaccine composition comprising a compound as defined in claim 6, or a pharmaceutically acceptable salt thereof, and an antigen or antigen composition.
 21. A method of treatment of an allergic disease or other inflammatory condition, an infectious disease or cancer, which method comprises administering to a human subject in need thereof, a therapeutically effective amount of a compound as defined in claim 6, or a pharmaceutically acceptable salt thereof.
 22. A method of treatment of allergic rhinitis, which method comprises administering to a human subject in need thereof, a therapeutically effective amount of a compound as defined in claim 6, or a pharmaceutically acceptable salt thereof.
 23. A method of treatment of asthma, which method comprises administering to a human subject in need thereof, a therapeutically effective amount of a compound as defined in claim 6, or a pharmaceutically acceptable salt thereof. 